ATM technology is playing an increasingly important role in future broadband networks and it is expected that there will be an emergence of "wireless ATM" networks enabling multimedia access for mobile end systems. Consequently, mobility support in an ATM network assumes increasing importance.
Wireless personal communication services (PCS) and broadband networking for delivery of multimedia information represent two well-established trends in telecommunications. While technologies for PCS and broadband communications have historically been developed somewhat independently, harmonization into a single architectural framework is motivated by an emerging need to extend multimedia services to portable terminals, as well as by service integration and operational efficiency considerations. Now that ATM is viewed as a universal base technology for broadband networks, it is reasonable to consider extension of standard ATM services into next-generation microcellular wireless/PCS scenarios. D. Raychaudhuri and N. D. Wilson, in an article entitled "ATM-Based Transport Architecture for Multiservices Wireless Personal Communication Networks," IEEE Journal on Selected Areas of Communications, vol. 12, no. 8, 1994, pp.1401-1414 and in an article entitled "Multimedia Transport in Next Generation Personal Communication Networks," Proc. of ICC, May 1994, pp. 858-862, propose an architecture for "wireless ATM" in which broadband services are extended over shared radio channels via incorporation of suitable medium access control (MAC) and data link control (DLC) layers into the standard ATM protocol stack. Medium access control is the subject of U.S. patent application Ser. No. 08/495,164 entitled "Multiservices Medium Access Control Protocol for Wireless ATM System" and data link control is the subject of U.S. patent application Ser. No. 08/553,168 entitled "Data Link Control Protocols for Wireless ATM Access Channels," both assigned to the same assignee as the present invention, and both incorporated herein by reference. The present invention concerns the related signaling, syntax and protocols required to support mobility in such a wireless ATM system. While some early work on the handoff aspects has been reported by A. Acampora and M. Nahshineh in an article entitled "An Architecture and Methodology for Mobile-Executed Handoff in Cellular ATM Networks," IEEE Journal on Selected Areas of Communications, vol. 12, no. 8, pp. 1365-1375, 1994 and by L. V. Hauwemeiren et al in an article entitled "Requirements for Mobility Support in ATM," Proc. of Globecom, 1994, pp. 1691-1694, further conceptual development is required to define a complete framework for handoff control in ATM.
Once a connection has been established between a source and a terminal, current protocols assume that the connection paths does not change during the period of a communication lifetime. This assumption is invalid when the terminal is a mobile terminal. In such cases, special handoff protocols are required.
The key issues in the design of efficient handoff protocols are:
1. During the re-routing of active connections, it is necessary to insure that minimal cells are lost. PA1 2. Determination of an optional cross-over joint (from where to re-route an existing connection to the new mobile terminal) is crucial to the quality of the re-routed connection. PA1 3. Before a mobile terminal can change, it is necessary to determine that the quality of service (QOS) contacts for the existing connection can be met at the new terminal, i.e. the call admission control (CAC) module is ready to accept the re-routed connection. PA1 4. A mobile terminal may have multiple active connections to one or more terminals where it is handed off. The connection can either be re-routed indirectly or may be re-routed/extended as a group.
The present invention provides efficient handoff techniques to support mobility within an ATM network. As an ATM signal is handed off from a first mobile terminal to a second mobile terminal, there is either a partial path re-routing of the signal from a source to the second mobile terminal or there is a path extension to the second mobile terminal.
U.S. Pat. No. 5,487,065 entitled "Method and Apparatus for Supporting Mobile Communications in Asynchronous Transfer Mode Based Networks" describes an ATM based network where the handoff is distributed, as contrasted with centralized. A communication route is determined which includes a connection from a base station via a switching node. A connection tree is determined to include potential connection from other base stations to the switching node. When the mobile user moves from one cell to another, corresponding to a change in base stations within the connection tree, the call is automatically handed over or rerouted to another route within the connection tree. The present invention does not require the creation of a static connection tree, and instead, dynamically extends or re-routes to an existing connection as the mobile endpoint changes its location.